UIInterfaceOrientation, CGAffineTransform, Frame, Bounds and Center

Can somebody point me to a good primer on the above, and what happens to one when you mess with the others? It seems as though no matter what I do, once I start messing with either the status bar orientation or the view transform (even if all I'm doing is 90-degree rotations), I can count on my views ending up sideways, upside down and backwards, and on a frustrating afternoo开发者_Go百科n of trial and error trying to get them straightened out. I'm sure it all makes sense once you know the logic and what order everything's applied in, but so far, empirically, I haven't been able to figure it out.

I don't know of a good single document primer on the subject, but the following is what I've learned from experience and reading the docs.

center, bounds, and frame

If you set frame then center and bounds will be updated. If you set center or bounds then frame will be updated. Frame is a convenience method for manipulating center and bounds using the superview's coordinate system.

From UIView Class Reference:

The geometry of a view is defined by its frame, bounds, and center properties. The frame defines the origin and dimensions of the view in the coordinate system of its superview and is commonly used during layout to adjust the size or position of the view. The center property can be used to adjust the position of the view without changing its size. The bounds defines the internal dimensions of the view as it sees them and is used almost exclusively in custom drawing code. The size portion of the frame and bounds rectangles are coupled together so that changing the size of either rectangle updates the size of both.

See The Relationship of the Frame, Bounds, and Center Properties for more details.

transform

If you set the transform property to something besides the identity transform, frame is undefined. If you set the transform to something else, you should only manipulate the view geometry using center (to position the view in it's superview) and bounds (to adjust the size of the view). Here's the relevant info from UIView Class Reference:

The origin of the transform is the value of the center property, or the layer’s anchorPoint property if it was changed. (Use the layer property to get the underlying Core Animation layer object.) The default value is CGAffineTransformIdentity.

...

Warning If the transform property is not the identity transform, the value of this property is undefined and therefore should be ignored.

See Coordinate System Transforms for more details.

UIInterfaceOrientation

UIInterfaceOrientation doesn't affect the transform, bounds, center, or frame properties directly. However, when the device orientation changes, the view controller will automatically resize its subview (which will in-turn resize it's subviews and so on).

See Responding to Device Orientation Changes and View Controller View Resizing for more details.